Empirical Freundlich Isotherm Research Articles

Preparation and application of a surfactant‐modified Halloysite nanotubes for the adsorption of nitrates from aqueous solutions: Kinetic and equilibrium studies

AbstractThe current research proposes the hexadecyltrimethylammonium bromide‐modified Algerian halloysite nanotubes (HNTs‐CTAB) as adsorbent for nitrate ions removal from aqueous solution via electrostatic interactions. X‐ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier‐transform infrared spectroscopy (FT‐IR), and nitrogen adsorption–desorption analysis techniques have been used to characterize the prepared adsorbants. The different operating condition that may affect the adsorption of nitrate was carried out. HNTs and HNTs‐CTAB adsorption capacities are considerably pH dependent. The optimum conditions for maximum removal of nitrate from aqueous solution were as follows: adsorbent masse was 40 mg, initial pH was 4, temperature was 25°C, initial nitrate concentration of 100 mg/L and equilibrium time was 3 h. Under optimal value of process parameters, maximum NO3− adsorption capacity of 47.4 mg/g was obtained. Kinetic investigation confirmed that the nitrate adsorption on modified HNTs followed a pseudo‐second‐order with correlation coefficients greater than 0.98 (R2 = 0.9870) and that empirical Freundlich isotherm was best fitted nitrate equilibrium adsorption. The thermodynamic studies indicated that the adsorption of nitrate onto HNTs‐CTAB is endothermic and spontaneous. HNTs‐CTAB displayed high regeneration ability by retaining a capacity above 40 mg/g after four reuse cycles. HNTs‐CTAB containing plentiful nitrate could be returned to the soil directly as an economic slow release fertilizers or a soil amendment due to its environmental‐friendly performance. Therefore, HNTs‐CTAB used for remediation of wastewater might be employed easily as farmland fertilizer.

Interaction of soil humic acids with gold ions and pathfinder elements

The study aims at experimental modeling of interaction of gold, arsenic, copper and lead ions with humic acids. The relevance and choice of the research objects are attributed to the poor coverage of characteristics of the mentioned ions with regard to their sorption interaction with humic acids. Arsenic, copper and lead are, on the one hand, common pollutants accumulated in soils exposed to anthropogenic impact and, on the other hand, are pathfinder elements for gold, which serve as indicators of gold mineralization in geochemical prospecting in secondary halos. The experiment has been carried out with the solution concentration ranging from 5 to 100 μg/cm3 at the temperature of 298 K. The adsorption isotherms obtained experimentally are described through the empirical Freundlich adsorption isotherm equation and the Langmuir adsorption model. A model experiment has been conducted on the effect of iron (III) ions on gold ion sorption, which is essential for determining the forms of gold in loose deposits in the presence of iron oxides and hydroxides. It has been shown that an increase in the iron concentration has practically no effect on the amount of sorbed gold ions in the concentration range under study.

Selective adsorption and removal ability of pine needle-based activated carbon towards Al(III) from La(III)

Rare earth elements are an important strategic resource. As one of the most valuable member, lanthanum plays a key role in lanthanide. However, trace Al(III) impurity in lanthanum materials can seriously damage the performance of lanthanum materials. In this paper, a nitrogen-containing activated carbon, AC-PN-700, was synthesized using pine needle as raw material and KOH as activator. The AC-PN-700 was characterized by surface area analyzer, elemental analysis and FT-IR. The adsorption and selective ability of AC-PN-700 towards Al(III) were investigated. The BET specific surface area of AC-PN-700 was 596.4 m2.g−1, and the average pore diameter was 2.7 nm. Depend on its large specific surface, well-developed internal pore structure and abundant nitrogen-containing functional groups, the AC-PN-700 possesses strong adsorption affinity and excellent recognition selectivity towards Al(III). The adsorption capacity of AC-PN-700 towards Al(III) could reach to 3.89 mg.g−1, removal rate towards Al(III) was almost 100%, and relative selectivity coefficients with respect to La(III) is 9.5. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. In addition, AC-PN-700 possesses better regeneration ability and reusability.

Degradation and adsorption of tralkoxydim in Chinese soils and water-sediment environments.

Tralkoxydim is a cyclohexanedione herbicide primarily used for gramineous weed control in China. In this paper, we present results of a tralkoxydim laboratory environmental fate study characterizing its degradation, adsorption, and mobility behavior in three different soils and two water-sediment systems (river and lake) in China. Degradation half-life of tralkoxydim in soil under aerobic conditions was 5.1, 7.7, and 7.9days in Jiangxi red soil, Taihu paddy soil, and Northeast China black soil, respectively. Under anaerobic and flooding conditions, half-life values were 6.2, 15.1, and 19.8days for the same three soils, respectively. Soil pH was the major factor effecting tralkoxydim degradation. In the aerobic water-sediment experiments, tralkoxydim degraded faster in the river system (total system half-life 43.3days) than the lake system (total system half-life 99.0days). Correspondingly, its anaerobic degradation half-life values were 46.2 and 53.3days for the river and lake systems, respectively. Tralkoxydim adsorption in the three soils was found to follow the empirical Freundlich isotherm. The adsorption coefficient (K d ) was 8.60, 1.00, and 1.57 for Jiangxi red soil, Taihu paddy soil, and Northeast China black soil, respectively. Soil pH was the major factor effecting tralkoxydim adsorption. Adsorption free energy change was less than 40kJmol-1 in all three soils, indicating a physical mechanism in the process. Thin-layer chromatography (TLC) tests showed that relative to the solvent transport to 11.5cm, the travel distance of tralkoxydim was 8-10cm in the three soils, corresponding Rf values at 0.05, 0.35, and 0.75 for Jiangxi red soil, Taihu paddy soil, and Northeast China black soil, respectively. Results of this work suggest that under alkaline conditions, tralkoxydim adsorption becomes smaller; thus, assessments on its mobility and potential groundwater impact should focus on these soil types.

Graphene materials for lead (II) extraction: an equilibrium study

The present paper describes a study on the adsorption of lead (II) ions on graphene materials obtained via exfoliation of a hydrolyzed expanded graphite intercalation compound. An equilibrium studies were performed implementing the empirical Freundlich and Langmuir isotherm models. It was found that all the isotherms are fitted well by those models, indicating the efficiency of the graphene materials as an adsorbent of heavy metals. The applicability of the two isotherms for sorption processes shows that both monolayer adsorption and heterogeneous energetic distribution of active sites on the adsorbent surface may take place. The maximum experimental lead (II) adsorption capacities of the materials under study – few-layered oxidized graphene suspension, multi-layered graphene paste, and few-layered graphene paste – were found to be 850, 230 and 170 mg/g, respectively. Due to the high sorption characteristics and unique physical and chemical properties of these materials, the adsorption technologies developed herein can act as good sustainable options for the future in heavy metal removal from industrial effluents.

Response surface modeling and optimization of nitrate removal from aqueous solutions using magnetic multi-walled carbon nanotubes

In this paper, the application of magnetic multi-walled carbon nanotubes (MMWCNTs) was studied for the removal of nitrate from aqueous solutions. MMWCNTs and Multi-walled carbon nanotubes (MWCNTs) are characterized by XRD, TEM, FT-IR, and VSM. The XRD results confirm that MWCNTs/Fe3O4 nanocomposites were successfully synthesized by a facile hydrothermal method. The MMWCNTs can be easily manipulated in a magnetic field for the desired separation, leading to the removal of nitrate from aqueous solution. In this study, the application of response surface methodology (RSM) is presented for optimizing the removal of nitrate from aqueous solutions using MMWCNTs. The effects of D/C (adsorbent dosage per initial concentration of pollutant ((mg) adsorbent/(mg/l) initial)) and initial pH on nitrate removal (%) were evaluated by RSM. Using RSM methodology, a quadratic polynomial equation was obtained for removal of nitrate by multiple regression analysis. The optimum conditions for maximum removal of nitrate from aqueous solution were as follows: D/C (40 (mg)/(mg/l)) and initial pH=4. Under optimal value of process parameters, maximum removal (97.15%) was obtained. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. The adsorption capacity amount of nitrate could reach up to 183.11mg/g at the high range concentration (50–100mg/l). It was found out that the MMWCNTs can be considered as a promising adsorbent for removal of nitrate from aqueous solution.

Removal of 2,4,6-trinitrotoluene from wastewater using a novel adsorbent polyvinyl alcohol/SiO2

2,4,6-Trinitrotoluene (TNT) is toxic and mutagenic to many living organisms, so more and more rigorous limits on the letting amount of TNT have been established. In this paper, monomer vinyl acetate (VAc) is grafted step by step on the surface of silica gel particles, and the grafted particle PVAc/SiO2 is formed. Then, the novel adsorbent polyvinyl alcohol (PVA)/SiO2 possessing strong adsorption ability for TNT is obtained through the alcoholysis reaction of PVAc. The grafted particles PVAc/SiO2 and PVAc/SiO2 are characterized by Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The adsorption performance of PVA/SiO2 toward 2,4,6-trinitrotoluene (TNT) is investigated through static methods. The experimental results show that PVA/SiO2 possesses strong adsorption ability for TNT with adsorption amount of 18.21 mg g−1. The empirical Freundlich isotherm is also found to agree well with the equilibrium adsorption data. In addition, pH is found to have great influence on the adsorption amount. Finally, PVA/SiO2 is found to have excellent reusability.

Sorption of phosphate onto mesoporous γ-alumina studied with in-situ ATR-FTIR spectroscopy

BackgroundDue to the extensive use of phosphates in industry, agriculture and households, the phosphate - γ-alumina interactions are important for understanding its detrimental contribution to eutrophication in lakes and rivers. In situ Fourier transform infrared (FTIR) spectroscopy can provide more detailed information on the adsorbate-adsorbent interaction and the formation of hydrogen bonds.ResultsIn situ ATR-FTIR spectroscopy was used to identify phosphate complexes adsorbed within the three-dimensional network of mesoporous γ-alumina at pH 4.1 and 9.0. The integrated intensity between 850 cm-1 and 1250 cm-1 was used as a relative measure of the amount of adsorbed phosphate. The integrated intensity proved to be about 3 times higher at pH 4.1 as compared with the corresponding intensity at pH 9.0. The adsorption of phosphate at the two pH conditions could be well described by the Langmuir adsorption isotherm at low concentrations and the empirical Freundlich adsorption isotherm for the whole concentration range, viz. 5 – 2000 μM.ConclusionsFrom the band shape of infrared spectra at pH 4.1 and pH 9.0, it was proposed that the symmetry of the inner-sphere surface complex formed between phosphate and γ-alumina was C1 at the lower pH value, whilst the higher value (9.0) implied a surface complex with C2v or C1 symmetry. The difference in adsorbed amount of phosphate at the two pH values was ascribed to the reduced fraction of ≡ AlOH2+ surface sites and the increased fraction of ≡ AlO- sites upon increasing pH from 4 to 9.

Binding and recognition ability of molecularly imprinted polymer toward p‐nitrophenol

Abstractp‐Nitrophenol is a hazardous phenolic compound and its separation and determination is very necessary to protect public health and environmental quality. In this article, macromolecule polyethyleneimine (PEI) grafted on the surface of silica particles was crosslinked using p‐nitrophenol as a template and diepoxyalkyl (669) as a crosslinking agent, and molecularly imprinted polymer on the surfaces of silica gel MIP‐PEI/SiO2 was prepared. The binding and recognition ability of MIP‐PEI/SiO2 for p‐nitrophenol were researched using batch and dynamic methods. The experimental results showed that MIP‐PEI/SiO2 had high affinity, specific recognition ability, and excellent selectivity for p‐nitrophenol. The saturated binding amount could reach to 155.5 mg g−1. The selectivity coefficients relative to m‐nitrophenol and chlorophenol were 45.80 and 117.5, respectively. The empirical Freundlich isotherm was found to describe well the equilibrium binding data. pH of sample solution was found to have a strong influence on the binding amount. MIP‐PEI/SiO2 was regenerated easily using diluted hydrochloric acid solution as eluent and MIP‐PEI/SiO2 possesses better reusability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The Adsorption Behavior of Functional Particles Modified by Polyvinylimidazole for Cu(II) Ion

AbstractIn this paper, a novel composite material the silica grafted by poly(N‐vinyl imidazole) (PVI), i.e., PVI/SiO2, was prepared using 3‐methacryloxypropyl trimethoxysilane (MPS) as intermedia through the “grafting from” method. The adsorption behavior of metal ions by PVI/SiO2 was researched by both static and dynamic methods. Experimental results showed that PVI/SiO2 possessed very strong adsorption ability for metal ions. For different metal ions, PVI/SiO2 exhibited different adsorption abilities with the following order of adsorption capacity: Cu2+ > Cd2+ > Zn2+. The adsorption material PVI/SiO2 was especially good at adsorbing Cu(II) ion and the saturated adsorption capacity could reach up to 49.2 mg/g. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. Higher temperatures facilitated the adsorption process and thus increased the adsorption capacity. The pH and grafting amount of PVI had great influence on the adsorption amount. In addition, PVI/SiO2 particles had excellent eluting and regenerating property using diluted hydrochloric acid solution as eluent. The adsorption ability trended to steady during 10 cycles.

Adsorption mechanism and property of novel composite material PMAA/SiO 2 towards phenol

In this paper, functional macromolecule poly(methacrylic acid) (PMAA) was grafted on the surface of silica gel particles using 3-methacryloxypropyl trimethoxysilane (MPS) as intermedia, and the grafted particle PMAA/SiO 2 with strong adsorption ability for phenol was prepared. The adsorption mechanism and properties of PMAA/SiO 2 for phenol were researched by static and dynamic methods. The experimental results showed that PMAA/SiO 2 possesses strong adsorption ability for phenol with interaction of three kinds of hydrogen bonds including peculiar O–H⋯π hydrogen bond (aromatic hydrogen bond) and O–H⋯O C π hydrogen bond. The saturated adsorption amount could reach up to 162.88 mg g −1. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. pH and temperature were found to have great influence on the adsorption amount. Finally, PMAA/SiO 2 was observed to possess excellent reusability properties as well.

Adsorption mechanism and property of a novel adsorption material PAM/SiO 2 towards 2,4,6-trinitrotoluene

2,4,6-Trinitrotoluene (TNT) is toxic and mutagenic to many living organisms, so more and more rigorous limits on the letting amount of TNT have been established. In this paper, functional monomer acrylamide (AM) was grafted step by step on the surface of silica gel particles, and the grafted particle PAM/SiO 2 with strong adsorption ability for TNT was formed. The adsorption mechanism and properties of PAM/SiO 2 for TNT were researched through static and dynamic methods. The experimental results showed that PAM/SiO 2 possesses strong adsorption ability for TNT with interaction of three kinds of hydrogen bonds including peculiar N H⋯π hydrogen bond (aromatic hydrogen bond) and C H⋯O C π hydrogen bond. The saturated adsorption amount could reach to 0.873 mg g −1. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. In addition, the pH and temperature were found to have great influence on the adsorption amount. Mixture solution of HCl and ethanol is used as eluent, and the adsorbed TNT is eluted easily from PAM/SiO 2. Finally, PAM/SiO 2 was found to have excellent reusability.

Adsorption performance and mechanism of 2,4,6-trinitrotoluene on a novel adsorption material polyvinylbenzyl acid/SiO 2

Polyvinylbenzene (PVB, namely polystyrene, PSt) was grafted on the surface of silica gel particles by “grafting from” in solution polymerization system, and grafting particles PVB/SiO 2 were obtained. The chloromethylation reaction of the grafted polyvinylbenzene was performed using a novel chloromethylation reagent, 1,4-bis (chloromethyoxy) butane that is un-carcinogenic, and grafting particles CMPVB/SiO 2 were obtained. Subsequently, chloromethyl groups on grafting particles CMPVB/SiO 2 were hydrolyzed and oxidized, and finally adsorption material polyvinylbenzyl acid/SiO 2 (PVBA/SiO 2) was prepared. The adsorption performances and mechanism of 2,4,6-trinitrotoluene (TNT) on PVBA/SiO 2 were investigated through static methods. The experimental results showed that PVBA/SiO 2 possessed strong adsorption ability for TNT with adsorption amount of 26.84 mg g −1. The empirical Freundlich isotherm was also found to agree well with the equilibrium adsorption data. In addition, pH was found to have great influence on the adsorption amount. Finally, PVBA/SiO 2 was observed to possess excellent reusability as well.

Adsorption of 2,4,6-trinitrotoluene on a novel adsorption material PEI/SiO 2

In this paper, functional macromolecule polyethyleneimine (PEI) was grafted onto the surface of silica gel particles in order to produce the novel adsorption material, PEI/SiO 2. Then this novel material's adsorption properties for TNT were investigated through static methods, and the experimental results showed that PEI/SiO 2 possessed strong adsorption ability for TNT. In fact, the saturated adsorption amount could reach 14.47 mg g −1. The empirical Freundlich isotherm was also found to describe well the equilibrium adsorption data. In addition, the pH and temperature were found to have great influence on the adsorption amount. Finally, PEI/SiO 2 was observed to possess excellent reusability properties as well.

Adsorption and recognizing ability of molecular imprinted polymer MIP-PEI/SiO 2 towards phenol

Firstly, functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles via the coupling grafting method, the adsorption material PEI/SiO 2 was formed. Secondly, the molecular imprinting was carried out towards the macromolecule PEI grafted on the surface of silica particles using phenol as a template and diepoxyalkyl (669) as a crosslinking agent. Finally, imprinted polymer MIP-PEI/SiO 2 with high affinity, specific recognition ability and excellent selectivity for phenol was prepared. The adsorption and recognition ability of MIP-PEI/SiO 2 for phenol were researched by static methods. The experimental results show that MIP-PEI/SiO 2 possesses very strong adsorption and recognition ability for phenol. The saturated adsorption capacity could reach to 46.6 mg g −1. The selectivity coefficients relative to resorcin and p-nitrophenol are 35.41 and 37.40, respectively. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. pH and temperature have great influence on the adsorption capacity. Diluted hydrochloric acid solution is used as eluent, and the adsorbed phenol is eluted easily from MIP-PEI/SiO 2.

Adsorption of phenol on a novel adsorption material PEI/SiO 2

In this paper, functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles via the coupling effect of γ-chloropropyl trimethoxysilane (CP), and the novel adsorption material PEI/SiO 2 with strong adsorption ability for phenol was prepared. The adsorption properties of PEI/SiO 2 for phenol were researched by both static and dynamic methods. The experimental results show that PEI/SiO 2 possesses very strong adsorption ability for phenol, and the saturated adsorption amount could reach to 160 mg g −1. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. pH and grafting amount of PEI have great influence on the adsorption amount. Diluted sodium hydroxide solution is used as eluent, and the adsorbed phenol is eluted easily from PEI/SiO 2.

Adsorption of Cd(II) from aqueous solution onto pyrite

The physicochemical factors such as equilibrium time, solution pH, initial concentration of Cd(II), particle size and temperature that control the adsorption of Cd(II) from aqueous solutions onto pyrite has been investigated through batch experiments. Prior to this study, pyrite was characterized through chemical and XRD-analysis. The point of zero charge, pH pzc was determined using the batch equilibrium technique and was found to be 6.4. The equilibrium time was 30 min at the solution pH of 6.0. The pH influence of Cd(II) adsorption was remarkable and maximum metal uptake was observed at 6.0 which is closer to pH pzc. Under this weakly acidic condition Cd(II) ions are responsible for adsorption. Concentration dependence of metal uptake indicates that saturation of pyrite surface by adsorbate occurs at an initial Cd(II) concentration of 350 mg/L and the corresponding metal uptake was 576.5 mg/L of −150 mesh size pyrite at pH 6.0 and 30 °C. Particle size affects the adsorption capacity to a great extent and a decrease in particle diameter enhances metal uptake. The effect of temperature on adsorption performance reveals that the effective temperature for Cd(II) adsorption is 30 °C. The empirical Freundlich isotherm was applied to represent the adsorption process, which fits the experimental data quite well. The work reveals that natural pyrite is a very good choice as an adsorbent for the removal of toxic metals from industrial wastewater and bears significant industrial implications.

Adsorption of an Amphoteric Aromatic Compound (p-Aminobenzoic Acid) onto Different Polymeric Adsorbents

The adsorptive properties of p-aminobenzoic acid onto macroporous, hypercrosslinked and multi-functional polymeric adsorbents were investigated systematically in the present study in relation to the particular physicochemical characteristics of an aromatic amphoteric compound containing both Lewis acid and Lewis base functional groups. A comparison of the thermodynamic and kinetic behaviours of the adsorbate towards three different polymeric adsorbents was made. It was found that the equilibrium adsorption data for the three polymeric adsorbents were well fitted by the empirical Freundlich isotherm. The results showed that the adsorption capacity of the multi-functional polymeric adsorbent NJ-99 was the largest among the three adsorbents studied. This may be attributed to strong hydrogen-bonding interaction and electrostatic interaction between the amino groups on the resin and the carboxyl group of p-aminobenzoic acid. In contrast, because of its smaller micropore volume, the adsorption capacity of macroporous XAD-4 was lower than that of the hypercrosslinked adsorbents CHA-111 and NJ-99. Calculation of the sorption enthalpy changes enabled the adsorption mechanism to be interpreted. In addition, a kinetic study of the sorption of p-aminobenzoic acid onto NJ-99 was also undertaken. The results showed that the adsorption process was mainly controlled by intraparticle diffusion.

Role of amination of a polymeric adsorbent on phenol adsorption from aqueous solution

Adsorption of seven phenols, one aromatic carboxylic acid and one sulfonated aromatic acid from aqueous solution, by a hypercrosslinked polymeric adsorbent (CHA-111) and the derivative animated by dimethylamine was compared. The results of different adsorption isotherms indicated that amino group on the polymeric matrix played a significant role on adsorption of almost all the employed compounds. For most employed compounds adsorption capacities increase to different degree and significantly for those with lower value of pKa. It may be attributed to the enhanced adsorbent–adsorbate interaction for amino group introduced on the polymeric matrix. The empirical Freundlich isotherm equation was employed to interpret the adsorbent–adsorbate interaction. The adsorption enthalpy change indicated the uptake of phenols on MCH-111 to be an enhanced physical adsorption because of the hydrogen-bonding interaction. Adsorption kinetic study of phenols on CHA-111 and MCH-111 was also conducted and amino group on the matrix will reduce the adsorption rate for change of pore size distribution and loss of macroprous volume as well as the hydration effect on the surface partly.

Adsorption of phenol and m-chlorophenol on organobentonites and repeated thermal regeneration

Experimental investigations were conducted on the adsorption characteristics of phenol and m-chlorophenol by organobentonites. The organobentonites were prepared by modifying natural bentonite with various quaternary ammonium salts including tetramethylammonium bromide, hexadecyltrimethylammonium bromide, benzyl-triethylammonium bromide, tetraethylammonium bromide and cetylpyridinium bromide. The adsorption characteristics of phenol and chlorophenol by these organobentonites were examined in detail. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. Thermal regeneration of spent organobentonites was also investigated and operating conditions of 200°C and 2 h heating were found to yield very good results.